A heat exchanger, for example as disclosed in Japanese Patent Publication No. 2003-314987, is known in the art, in which refrigerant is heat exchanged with air. The heat exchanger comprises a core portion having multiple tubes and a pair of tanks (header tanks) fixed to the tubes, wherein the tubes and the tanks are made of separate units and both end portions of the tubes are inserted into the tanks so that passages formed in the tubes are communicated with insides of the tanks.
A width of the tank (a width in an air flow direction) must be made larger than a width of the tubes, because both ends of the tubes are inserted into and fixed to the tanks.
A fluid passage portion is formed in the tanks and a width of the fluid passage portion (in the air flow direction) is made smaller than the width of the tubes, to make the evaporator smaller in its size.
In the case that the multiple tubes are arranged to vertically extend, the tanks are respectively located horizontally at vertical ends of the core portion (at upper and lower ends of the tubes).
When refrigerant is evaporated in the evaporator by absorbing heat from air passing through outside surfaces of the tubes of the core portion, condensed water is generated at the core portion, flows down along the tubes and reaches at an upper surface of the lower tank.
In the conventional evaporator, the condensed water can not be easily drained out from the evaporator, when the lower tank has a larger width in an air flow direction than the width of the tubes. And the condensed water is likely to stay at a lower part of the core portion.